An optical tracking system may be used for tracking a target. Recently, in order to perform precise surgery while minimizing a risk of the surgical errors, a method has been used that tracks the location (or coordinates) and the posture (or orientation) of a surgical robot or a surgical instrument and utilizes the tracking result for surgery. The location of a target, for example, may be defined as spatial coordinates, such as coordinates on the X, Y, and Z axes of an orthogonal coordinate system. The posture of a target may be defined as a roll, pitch, or yaw. In order to accurately track a target, it is important to accurately recognize the location and the posture of the target, which correspond to six degrees of freedom as described above.
In the optical tracking system, for example, after attaching a reference body, such as a marker, to the target, the marker is tracked in order to determine the location and the posture of the target. The optical tracking system goes through, for example, a process in which a part of the marker is imaged using an image capturing device such as a camera or the like, and the image is read. In this process, a part of the captured image (for example, a boundary portion) may appear blurred or unclear due to various factors. When the marker is tracked based on such an image, there may be generated a difference between the estimated location and posture of the target and the actual location and posture of the target.